1. Field
The present invention relates to point to multi-point communications systems. More specifically, the present invention relates to a method and apparatus for forming an ad-hoc location-based multicast group.
2. Background
In emergency communication situations, such as those arising from natural or man-made disasters, it is critical to enable forms of communication that are efficient, so that maximum number of affected people can access limited resources, such as wireless telecommunication channels. At times of large-scale disasters (e.g. earthquake or hurricanes), communication resources can be subjected to an unusually high load. A class of wireless service intended for quick, efficient, one-to-one or one-to-many (group) communication has existed in various forms for many years. In general, these services have been half-duplex, where a user presses a “push-to-talk” (PTT) button on his phone/radio to initiate speech. Pushing the button either keys his radio, in some implementations, or in a moderated system, where communications occurs via a server of some type, indicates the user's request for the “floor.” If granted the floor, or talker permission, the user then generally speaks for a few seconds, after which he releases his PTT button, and other speakers can request the floor. Communication is generally from one speaker to a group of listeners, but may be one-to-one. This service has traditionally been used in applications where one person, a “dispatcher,” needs to communicate to a group of people, such as field service personnel or taxi drivers, which is where the “dispatch” name for the service comes from.
A key feature of these services is that communication is quick and spontaneous, usually initiated by simply pressing a PTT button, without going through a typical dialing and ringing sequence. Communication in this type of service is generally very short, with individual talk “spurts” being generally on the order of several seconds, and “conversations” lasting possibly a minute or less.
Since communications occur in “spurts” or abbreviated conversations, the conveyed information is generally to the point and results in an efficient communication methodology for emergency conditions where communication resources may be limited. Accordingly, communications that occur in “spurts” only require an occasional allocation of the communication resources to a specific user or group of users, making the resources available for use of others at different times. It is known that the use of communication “spurts” rather than dedicated channels results in a more efficient use of resources as many dedicated resource conversations includes substantial amounts of transmitted silence. Additionally, half duplex conversations do not tax resources of the portion of the conversation, either listening or speaking, that is not being utilized at the time.
As stated, communication may be configured to occur among group members. In a dispatch model, communication between endpoints takes place within virtual groups wherein the voice of one “talker” is broadcast or more specifically “multicast” to one or more “listeners”. A single instance of this type of communication is commonly referred to as a dispatch call or simply a call. A call is an instantiation of a group, which defines the characteristics of the call and is, in essence, a member list with some associated information, such as a group name or group id. A member list is a list of one or more users that are invited to participate in the call.
There is a need for emergency response teams to establish communication with any and all users in an area affected by a large scale natural disaster, without straining available telecommunication resources excessively and for users in an area to be given emergency assistance information that is specific to the area where they are located.